Strengths
and weaknesses

It
images muscle and soft tissue
very well and is particularly
useful for delineating the interfaces
between solid and fluid-filled
spaces.

It
renders "live" images, where the
operator can dynamically select
the most useful section for diagnosing
and documenting changes, often
enabling rapid diagnoses.

It
shows the structure as well as
some aspects of the function of
organs.

It
has no known long-term side effects
and rarely causes any discomfort
to the patient.

Equipment
is widely available and comparatively
flexible; examinations can be
performed at the bedside.

Weaknesses
of ultrasound imaging:

Ultrasound
cannot penetrate bone and performs poorly when there
is air between the scanner and
the organ of interest. For example,
overlying gas in the gastrointestinal
tract often makes ultrasound scanning
of the pancreas difficult.

Even
in the absence of bone or air,
the depth penetration of ultrasound
is limited, making it difficult
to image structures that are far
removed from the body surface,
especially in obese patients.

The
method is operator-dependent.
A high level of skill and experience
is needed to acquire good-quality
images and make accurate diagnoses.

Doppler
ultrasonography

Ultrasonography
can be enhanced with Doppler measurements,
which employ the Doppler effect to assess
whether structures (e.g. blood)
are moving towards or away from
the probe. By calculating the frequency
shift of a particular organ, e.g.
the jet of blood flow over a heart
valve, its velocity and direction
can be determined and visualised.
This is particularily useful in
echocardiography (ultrasonography
of the heart) and essential in determining
reverse blood flow in the liver
vasculature in portal hypertension.

Edler
had asked Hertz if it was possible
to use radar to look into the body, but
Hertz said this was impossible.
However, he said, it might be possible
to use ultrasonography. Hertz was
familiar with using ultrasonic reflectoscopes
for nondestructive materials
testing, and together they developed
the idea of using this method in
medicine.

The
first successful measurement of
heart activity was made on October 29,
1953
using a device lent from the ship
construction company Kockums
in Malmö. On December 16 the same year,
the method was used to generate
an echo-encephalogram (ultrasonic
probe of the brain).
Edler and Hertz published their
findings in 1954.

Scotland

Parallel
developments in Glasgow, Scotland (coincidentally also
a major shipbuilding centre) by
Professor Ian
Donald and colleagues at the
Glasgow
Royal Maternity Hospital (GRMH)
led to the first diagnostic applications
of the technique. Donald was an
obstetrician with a self-confessed
"childish interest in machines,
electronic and otherwise", who,
having treated the wife of one of
the company's directors, was invited
to visit the Research Department
of marine boilermakers Babcock &
Wilcox at Renfrew, where he
used their industrial ultrasound
equipment to conduct experiments
on various morbid anatomical specimens
and assess their ultrasonic characteristics.
Together with the medical physicist
Tom Brown and fellow obstetrican
Dr John MacVicar, Donald refined
the equipment to enable differentiation
of pathology in live volunteer patients.
These findings were reported in
The Lancet
on 7th June 1958 as "Investigation
of Abdominal Masses by Pulsed Ultrasound"
- possibly one of the most important
papers ever published in the field
of diagnostic medical imaging.

At
GRMH, Professor Donald and Dr James
Willocks then refined their techniques
to obstetric applications including
fetal head measurement to assess
the size and growth of the foetus.
With the opening of the new Queen
Mother's Hospital on Yorkhill
in 1964, it became possible to improve
these methods even further. Dr Stuart
Campbell's pioneering work on fetal
cephalometry led to it acquiring
long-term status as the definitive
method of study of fetal growth.
As the technical quality of the
scans was further developed, it
soon became possible to study pregnancy
from start to finish and diagnose
its many complications such as multiple
pregnancy, fetal abnormality and
placenta praevia.
Diagnostic ultrasound has since
been imported into practically every
other area of medicine.